To date, for example, power module substrates in which a metal plate composed of a metal material, e.g., Cu, is bonded to the upper surface of an insulating substrate composed of a ceramic sintered body or the like have been used as circuit boards used for electronic apparatuses, e.g., a power module incorporated with electronic components e.g., an insulated gate bipolar transistor (IGBT).
The metal plate in the circuit board forms a circuit for electrically connecting an electronic component to an external electric circuit. The electronic component mounted on the circuit board is electrically connected to the metal plate, the electronic component is covered with a mold resin, and thereby, an electronic apparatus is produced. Regarding such an electronic apparatus, the electronic component and the external electric circuit are electrically connected to each other with the metal plate interposed therebetween.
Recently, a technique to use a silver grain sintered body for bonding an electronic component to a metal plate or the like has been proposed. Also, a technique to dispose a silver layer on the upper surface of a metal plate on which an electronic component is mounted for the purpose of suppressing formation of an oxide film on the metal plate surface has been proposed (refer to, for example, PTL 1).